1. Field of the Invention
The present invention relates generally to a method of preparing a surface for plating and a product thereof. More particularly, the invention is directed to a method of manufacturing a highly advantageous circuit board substrate for plating a conductive material thereto and the circuit board product thereby.
2. Brief Description of the Prior Art
The evolution of the printed circuit board has progressed at an accelerated pace over the last 25 years. In this regard, a number of processes and resultant printed circuit boards have been suggested to meet the demands of modern industry. A particularly vexing problem has been the adherence, or affixing, of a conductive metallic layer to the insulating substrate. Generally, the prior art has found that an adequate adhesion for a metal deposit is evidenced by a peel strength of at least 5 lbs./in. This problem has become more acute as the miniaturization of circuit boards has progressed. Other problems exist, such as the susceptibility of the conductive patterns to physical damage on the surface of the substrate, the strength of the circuit board, the economy of production, the desire to have a fire resistant substrate, adequate plating of holes, and the desire to have a relatively non-porous substrate surface between the conductive patterns.
The achievement of an optimum substrate surface for the affixing of the conductive layer to the substrate, while at the same time providing intermediate surface areas that are not absorbent, or porous, to moisture has been difficult. One approach has been to sandblast the normally glossy surface of a plastic resin substrate thereby roughing the surface to increase the adherence of the metal to the roughened portions of the surface. A refinement of this method is to mask the substrate area so that only the conductive pattern area is subject to the sandblast. Another approach, disclosed in the Cado U.S. Pat. No. 3,042,591, has been to provide serrations on the debossing dies to actually mold a serrated roughened surface into the substrate.
Another popular method of preparing a substrate surface is the swell and etch technique wherein the surface of the substrate is actually swelled and then etched with an appropriate chemical to degrade the plastic surface so that it is receptive to metal plating such as disclosed in the Dinella, et al., U.S. Pat. No. 3,758,332, and the Davis, et al., U.S. Pat. No. 3,560,241.
Another method as represented in the U.S. Pat. No. 3,666,549, granted to Rhodenizer, et al., the Grunwald U.S. Pat. No. 3,620,933, and the Watanabe U.S. Pat. No. 3,552,085 is the clad and strip process wherein the substrate is coated with an appropriate metal, such as copper, or aluminum, and then subsequently stripped to provide an irregular surface for affixing the desired conductive pattern.
Other approaches, such as the Mickelson, et al., U.S. Pat. No. 3,434,939 have used adhesive, or similar bonding agents, to fasten an electrically conductive metal to the substrate.
The Greenman, et al., U.S. Pat. No. 2,986,804 provides a three dimensional circuit board with appropriate ribs for reinforcing the board.
The Bell, et al., U.S. Pat. No. 2,925,645 discloses a process for adhering a metal foil to a plastic substrate. In this regard, powder particles are attached to the foil by adhesion or a technique of sintering. The foil is then pressed and heated to provide a mechanical bonding with the substrate surface.
The Luce, U.S. Pat. No. 3,293,109 discloses an irregular lamina surface coated with a copper foil. The Blessinger, et al., U.S. Pat. No 3,895,132 discloses a method of creating a random surface pattern on articles.
The Lando, U.S. Pat. No. 3,900,614, Shepard, U.S. Pat. No. 3,851,621, Parfet, U.S. Pat. No. 3,800,020, Wharton, U.S. Pat. No. 3,077,658, Malcolm, U.S. Pat. No. 2,772,501, McReadie, U.S. Pat. No. 2,955,351, Shipley, Jr., U.S. Pat. No. 3,011,920 and Tsu, et al., U.S. Pat. No. 3,212,918 are cited of general interest for various methods of making a printed circuit board.
The O'Shaughnessy, U.S. Pat. No. 3,897,387, Touval, U.S. Pat. No. 3,897,389, and Vogel, U.S. Pat. No. 3,897,346 are cited to disclose various flame retardant agents for synthetic plastics.
As can be appreciated by those skilled in the art, there is still a desire to provide an efficient and economical method of adhering a metal conductive layer to a non-conducting substrate which will adequately meet all the demands upon a printed circuit board that are presently being made by industry.